This proposal represents a unified and internally self-contained effort to solve the structure of a few specific cell membrane proteins by high resolution electron crystallography. Research during the 5-year period of this grant will focus on bacteriorhodopsin and the various intermediates in its photocycle, PhoE porin, LamB porin, the adenine nucleotide exchanged protein from mitochondria, and a plasma membrane proton ATPase. The Program possesses all technical expertise and research facilities required for isolation and purification of the desired proteins, for biophysical and biochemical characterization (and modification, as desired), for reconstitution as two-dimensional crystalline sheets and for crystallographic structure analysis. Collaboration with expert investigators at other institutions is however, pursued when duplication of effort would be wasteful and unproductive.